1) Field of the Invention
The invention relates to a connecting element for mechanically connecting constructive elements. It comprises an elastically deformable tensioning element which applies a holding force in its elastically deformed state, onto at least one constructive element connected by the connecting element, thus generating a nonpositive connection of at least one constructive element with the tensioning element or with another constructive element. In particular, the invention relates to the linking of longitudinal, wire-shaped constructive elements as e.g. profiles and tubes, also with small diameters in the range of a few millimeters or less. A connection is to be understood as the joint of a tensioning element to a constructive element to be connected, or the connection of two or more constructive elements to each other. In particular, the invention relates to the mechanical-connection of constructive elements consisting of a material which is difficult to weld or to solder, e.g. a nickel-titanium alloy.
2) Description of the Related Art
In many ranges of technology, there is the requirement to connect constructive elements mechanically, however, connections which allow detachment if necessary, are desired, too. A usual method is to use an elastically deformable tensioning element which applies a holding force in its elastically deformed state, onto one constructive element to be connected, thus generating a nonpositive connection of at least one constructive element with the tensioning element or with another constructive element. Principally, there are two ways of deforming the tensioning element elastically.
The first variant is to bring the tensioning element from a relaxed initial position into a pre-tensioned position by means of an elastic deformation, where it is deformed and elastically expanded. In the pre-tensioned position, the constructive element to be connected (at least one) can be inserted into the tensioning element (or, if necessary, vice versa, the tensioning element into the constructive element). After that, the tensioning element is allowed to return to a less tensioned position, where it applies a holding force, caused by the elastic deformation, onto the connected constructive element. This holding force generates the nonpositive connection.
The second possibility is to bring the tensioning element from its relaxed initial position into a tensioned position, where the mechanical tension generated by the expansion causes the holding force. The tensioning element can be pre-tensioned in an opposite direction before the insertion of the constructive element to be connected, if necessary.
Thus, as to the state of the art, it is known to fit coil springs made of steel to the ends of Allan keys; these coil springs are wound around the tip of the key in a way that the coil spring fixes the key in a non-positive way due to the spring load. With this, the key can be fixed to a bunch of keys by means of the coil spring. According to the first described variant, the coil spring is expanded for inserting the Allen key, and generates the holding force in a partially relaxed position. On the other hand, the coil spring can also be applied to the key by the second described variant, being contracted and decreasing the diameter, which presents similarities with crimping; this, too, generates a holding force by the winding around the key end.
Another known example from the state of the art are shrinking joint sleeves for the butt joining of tubes, e.g. according to the literature reference Engineering Aspects of Shape Memory Alloys, Duerig, Melton, Stöckel, Wayman, Verlag Butterworh-Heinemann Ltd., 1990 or according to DE 4026644 C1. Here, a shape memory alloy in form of a sleeve, with a suppressed shape memory effect, is located around the joint and shrunk. The entire usable shrinking effect amounts to approximately three to four percent after subtracting the installation tolerance, the substrate tolerance, the substrate deformation during shrinking and the suppressed shape memory effect; this makes it necessary to comply exactly with the tolerances in order to generate a reliable joint. These shrunk joints are based on a one-way effect, this means that the joints cannot be detached any more. The effect applied for joining during the shrinking process is based on a phase transformation, during which the metallographic structure of the shrinking sleeve changes.